\section{Efficient and robust replication}

In this section, we first present two novel replication protocols that provide
better robustness guarantees with slightly increasing overhead. And then we
discuss geo-replication and multiple replicated service coordination as future
works.

\subsection{Gnothi}
It tries to achieve the high availability and correctness guarantee of asynchronous
replication and the low cost of synchronous replication.

\subsection{Active storage}
It tries to tolerate arbitrary faults with $f+1$ replication.

\subsection{Geo-replication (future work)}

\subsection{Multiple RSMs (future work. If Manos is working on that, I will not put it here)} 